1. Field of the Art
This invention relates to an endoscope for use in medical examinations, and more particularly to an endoscope which is provided with an objective lens drive mechanism to move by remote control a plural number of lens groups of an optical objective lens system, which is incorporated into an observation window on a rigid tip end section of an elongated insertion instrument of the endoscope, for example, for adjustment of at least focal depth, image magnification rate or view field angle.
2. Prior Art
Generally, endoscopes which are in use for medical purposes are largely constituted by a manipulating head assembly to be gripped and manually operated by a hand of an operator, an elongated insertion instrument extended on the front side of the manipulating head assembly for insertion into a body cavity of a patient, and a universal cable which is led out from the manipulating head assembly and disconnectibly connected to a light source. For its functions, the elongated insertion instrument of an endoscope is successively constituted by, from its fore distal end, a rigid tip end section, an angle section and a flexible body portion. The flexible body portion occupies the major length of the elongated insertion instrument from a proximal end portion which is connected to the manipulating head assembly, and arranged to be bendable in arbitrary directions along a path of insertion. The rigid tip end section contains an illumination window or windows, an image pickup means, and an opening of a biopsy channel through which forceps or other instrument is introduced into a body cavity. The angle section is can be angularly bent by remote control from the manipulating head assembly, for turning the rigid tip end section into an arbitrary direction.
As mentioned above, the rigid tip end section contains at least an illumination window and an image pickup means. Located within the illumination window is a light emitting end of a light guide which is constituted by a bundle of fiber optics. The light guide is extended as far as the above-mentioned universal cable via the manipulating head assembly and disconnectibly connected to a light source. On the other hand, as the image pickup means, an optical objective lens system is fitted in an observation window on the rigid tip end section. In the case of an electronic endoscope, a solid-state image sensor device is located at the focus of the optical objective lens system. In the case of an optical endoscope, an image pickup end of a light guide, which is constituted by a bundle of fiber optics, is located at the focus of the optical objective lens system. A signal cable which is connected from the solid-state image sensor device or the image guide is passed through the insertion instrument along with the light guide and extended to the manipulating head assembly. An electronic endoscope which appears in the following description can be read and taken as an optical endoscope if a solid-state image sensor device and a signal cable is replaced by an image guide.
In addition to the above-mentioned component parts, an exit opening of a biopsy channel is provided on the rigid tip end section. Connected to the exit opening is a biopsy channel which is constituted by a flexible tube. Further, a wash nozzle is provided on the rigid tip end section to wash clean the observation window when contaminated. An air/water feed tube is connected to the wash nozzle. These biopsy channel and air/water feed tube are extended as far as the manipulating head assembly through the elongated insertion instrument of the endoscope.
As described above, an elongated insertion instrument of an endoscope is normally required to accommodate bundles of fiber optics, signal cable, biopsy channel and a number of feed tubes. In order to bend the angle section as described above, a pair of upper and lower operating wires or two pairs of vertical and horizontal operating wires are also passed through the insertion instrument. The fore ends of these operating wires are fixed either to the rigid tip end section or to a structural member in the proximity of the rigid tip end section. Within the angle section, the positions of the operating wires are restricted in circumferential direction. Further, the respective operating wires are extended as far as the manipulating head assembly through the flexible section of the endoscopic insertion instrument.
The optical objective lens system of the image pickup, which is normally constituted by a plural number of lenses, should preferably be capable of adjustments in focal depth, image magnification and view field angle, depending upon the position of an intracavitary portion to be examined or upon the purpose of examination. In this regard, it has been known to make part of the lenses of the optical objective lens system movable in the direction of optical axis for adjustments of focal depth, image magnification or view field angle.
As for drive means for moving a movable lens in the direction of optical axis of the objective lens system, there have been various proposals, including piezoelectric elements, shape memory alloys and artificial muscle. However, in actual applications, it has been the general practice to use a control cable for shifting the position of a movable lens or lenses by remote control. In such a case, the fore end of a control cables is connected to the movable lens, while the proximal end of the cable is extended into the manipulating head assembly in such a way that an operator can shift the position of a movable lens in the direction of optical axis by remote control from the head assembly. More particularly, a control cable of this sort is usually composed of a flexible sleeve and a number of transmission members which are fitted in the flexible tube. The transmission members are either in the form of push-pull type operating wires or in the form of a flexible rotation transmission shaft which is constituted by tightly wound coil tubes. In the case of push-pull wires, the fore end of operating wires are connected to a support member of a movable lens thereby to push or pull the movable lens. On the other hand, in the case of a flexible transmission shaft, a screw rod which is connected to the fore end of a flexible transmission shaft is engaged with a nut member which is provided fixedly on the part of a movable lens support member, for example, on a movable lens frame. Accordingly, in this case, a rotational movement of the flexible transmission shaft is translated into a linear movement of a movable lens. No matter whether the drive means employs the push-pull wires or a flexible transmission shaft, it can be arranged either as a manual drive or as a power drive having a motor or an actuator incorporated into a manipulating head assembly of an endoscope.
For instance, for varying an image magnification rate, it has been known to employ an objective lens system employing two lens groups, i.e., a variator lens and a compensator lens, which are movable in the direction of optical axis of the objective lens system independently of each other. In this instance, each one of the two lens groups is not necessarily composed of a plural number of lens elements, and can be composed of a single lens element. The two lens groups are moved in a different way from each other in distance, speed and direction. However, considering the smallness in diameter of the endoscopic insertion instrument, it has been found impossible to incorporate two independent drive means into the insertion instrument for the purpose of driving the two lens groups in different ways as mentioned above. In this connection, attempts have been made to provide movable lenses within a cam tube and to move a plural number of lenses concurrently in predetermined directions by rotating or linearly moving the cam tube, for example, as disclosed in Japanese Laid-Open Patent Application H11-42202. The drive mechanism according to this prior art employs a cam tube which is provided with a plural number of cam grooves in such a way as to circumvent lens tubes of an optical objective lens system. Lens frames of movable lenses are fitted in the cam tube, with pins on the lens frames in engagement with the cam grooves. The can tube is biased to protrude in the forward direction by the action of a biasing spring, while the cam tube can be pulled in the rearward direction along the circumferential surfaces of the lens tubes by pulling operating wires which are connected to the cam tube. Accordingly, by moving the cam tube in the forward or backward direction, the movable lenses are turned to shift their positions in the direction of optical axis.
An optical objective lens system which uses the above-mentioned prior art lens drive mechanism suffers from a drastic increase in diameter of an assembly of the objective lens system including the lens drive mechanism due to the use of the cam tube around lens tubes of the system in addition to a biasing spring and operating wires which are connected to the cam tube. Needless to say, a drastic increase in diameter is a detrimentally negative factor for an endoscopic insertion instrument.
Further, endoscopes are usually used for examination or observation within dark body cavities. Therefore, normally an illumination means is provided at the distal end of an endoscopic insertion instrument. However, since the insertion instrument is small in diameter, the illumination means is required to have a small aperture diameter and to project illumination light from an illumination window which is substantially in the form of a point light source. Therefore, an illumination lens is usually fitted in the illumination window to disperse the illumination light as much as possible. However, it has been found difficult to prevent variations in illumination level across a view field. Since a cam tube is fitted on lens tubes of an optical objective lens system of an image pickup, an illumination window or windows are necessarily located at a distant position from the image pickup. Consequently, at the time of observing an intracavitary portion in the proximity of a fore distal end of an endoscopic insertion instrument, there arises a problem that illumination light level drops conspicuously in a central region of an area under observation, failing to illuminate the whole view field sufficiently and uniformly.
A cam tube which is fitted on lens tubes needs to be driven from behind. Accordingly, operating wires and a biasing spring for the cam tube are located in positions behind the lens tubes. In this connection, in the case of an electronic endoscope, it is desirable for a solid-state image sensor device to have a broad image receiving surface area because the greater the number of its picture elements the higher becomes its resolution power. This means that the endoscopic insertion instrument should be provided with an image pickup means of a larger size including a solid-state image sensor device and its substrate board. In order to build in an image sensor device of a large size within increasing the outside diameter of the endoscopic insertion instrument, an image receiving surface of the solid-state image sensor device should preferably be disposed to face in the axial direction of the insertion instrument. For this purpose, it becomes necessary to bend a light path from an optical objective lens system through 90 degrees by the use of a prism which is located in a position behind lens tubes. Therefore, in case a cam tube is fitted on lens tubes, the prism may become an obstacle in connecting drive means to the cam tube and limit the size of the solid-state image sensor device to be used on the endoscopic insertion instrument.
In view of the difficulties as mentioned above, it is an object of the present invention to provide an endoscope with an objective lens drive mechanism which can shift positions of a plural number of movable lenses within a lens tube of an optical objective lens system smoothly in the direction of optical axis and without necessitating to increase the diameter of the lens tube to any conspicuous degree.
It is another object of the present invention to provide an endoscope with an objective lens drive mechanism which permits to locate illumination windows closely on opposite sides of an observation window of an image pickup portion, for illuminating a view filed of the image pickup substantially with a uniform light volume.
In accordance with the present invention, for achieving the above-stated objectives, there is provided an endoscope with an objective lens drive mechanism for an optical objective lens system mounted within an observation window on a rigid tip end section of an elongated insertion instrument of the endoscope, the optical objective lens system being composed of a plural number of lens groups including at least two movable lens groups to be moved in the direction of optical axis of the optical objective lens system, comprising: movable lens frames supporting the movable lens groups; ring members respectively connected to the movable lens frames and each provided with a radial cam pin on an inner peripheral side thereof; a cam shaft rotatably supported on the rigid tip end section in parallel relation with the optical objective lens system, and formed with cam grooves on circumferential surfaces thereof for engagement with cam pins on the ring members; and a drive means coupled with the cam shaft for rotationally driving same in forward and reverse directions.
In one specific form of the invention, for planting the radial cam pins on the respective ring members, a stepped through hole is formed in each ring member a cam pin is threaded into the stepped hole to project on the inner periphery of the ring member, with a flanged head portion of the cam pin in engagement with an outer larger diameter portion of the stepped hole. Preferably, each ring member is further provided with a resilient cover of substantially C-shape which is adapted to cover the stepped hole from outside. In case of an electronic endoscope, a large image pickup means is often used to obtain picture images of higher resolution. In order to incorporate a large image pickup means without increasing the outside diameter of the rigid tip end section of the endoscopic insertion instrument, an image receiving surface of a solid-state image sensor device has to be positioned in such a way as to face the optical axis of the objective lens system. For this purpose, a prism is employed to bend a light path from the objective lens system through 90 degrees. Further, arms members are connected between the ring members and the lens frames to offset the positions of the ring members to a sufficient degree relative to the movable lens frames, locating the cam shaft in a position out of interference with the prism of the objective lens system. As for a drive means for the cam shaft, there may be employed a control cable using a flexible rotation transmission shaft. Alternatively, in order to make the internal construction of the insertion instrument more compact, an electric motor may be coupled with the cam shaft. In this case, an output shaft of an electric motor may be coupled with an input portion of the cam shaft through transmission gears. In this regard, it is preferable to provide a predetermined clearance between the output shaft of an electric motor and the input portion of the cam shaft to ensure smooth transmission of rotation. Furthermore, the cam grooves on the cam shaft are preferred to have an inclination angle in the range of from 5 to 30 degrees.
The above and other objects, features and advantages of the present invention will become apparent from the following particular description of the invention, taken in conjunction with the accompanying drawings which show by way of example some preferred embodiments of the invention.